Java Reference
In-Depth Information
You can find out how many indices already have elements by using the method
size
. If
list
is an
ArrayList
,
list.size()
returns the
size
of the
ArrayList
, which
is the number of elements stored in it. The indices of these elements go from
0
to
one less than
list.size()
.
size
The
size
Method
The method
size
returns the number of elements in an
ArrayList
.
EXAMPLE
for
(
int
index = 0; index < list.size(); index++)
System.out.println(list.get(index));
list
is an
ArrayList
object.
TIP: Summary of Adding to an
ArrayList
To place an element in an
ArrayList
position (at an
ArrayList
index) for the first
time, you usually use the method
add
. The simplest method named
add
has a single
parameter for the element to be added and adds elements at index positions
0
,
1
,
2
,
and so forth, in that order.
You can add an element at an already occupied list position by using the two-parame-
ter version of
add
. When inserting into an
ArrayList
with this version of
add
, elements
at the specified index and higher are moved up one position to make room for the new
element. For example, suppose
list
is an
ArrayList
object with base type
String
that
has three elements already on its list. Consider the following method invocation:
add
list.add(1, "Amor");
Before there were elements at index positions
0
,
1
, and
2
. When this invocation of add
is executed, the element
"Amor"
is inserted at index
1
, and the elements at index posi-
tions
1
and
2
are moved to positions
2
and
3
.
You can also use the two-argument version of
add
to add an element at the first
unused position. If
list
has elements at index positions
0
,
1
,
2
, and
3
, then the follow-
ing is legal:
list.add(4, "Mucho Amor");
Your code can then go back and change any individual element, using
set
. However,
set
can reset only the element at an index that already has an element.
The method
size
can be used to determine how many elements are stored in an
ArrayList
.
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